This invention relates to comminuted synthetic pigments and more particularly relates to a reduced structure silica or silicate pigment.
The art of adding fillers to various grades of paper dates back to the ancient days of paper making. Today, fillers such as titanium dioxide, synthetic sodium alumino silicates, clay, diatomaceous silica, calcium sulfate, calcium carbonate, calcium sulfite, calcium silicate, talc, etc. are used as fillers for various grades of paper. When used in the proper amounts, the pigment filler improves the quality of the paper and its optical properties. Fillers as a general rule are highly desirable in printing papers where they increase the brightness, opacity, and improve the surface and printability of the sheet.
Pigments are usually considered to be satisfactory for filling when they have a high degree of whiteness, a high index of refraction, small particle size, low solubility in water, chemical inertness, and low specific gravity. However, recent studies have shown that these criteria alone are not sufficient to predict the performance of a pigment in paper. Only when actually tested can the value of a pigment be determined.
The most-sought-after fillers for high quality paper or publication stock are those which improve the optical qualities of the sheet and reduce ink show-through at a relatively low pigment loading.
Usually, the most desirable filler pigments such as titanium dioxide and sodium alumino silicates are also the most expensive to manufacture and purchase. Clay and calcium carbonate are also used as fillers for publication stocks.
Titanium dioxide is particularly successful as a filler pigment in high quality papers because of the whiteness of the pigment and the brightness and opacity it imports to paper. Unfortunately the cost of titanium dioxide is prohibitive in many situations where its desirable properties could be utilized.
A pigment which comes close to performing as well as titanium dioxide and which may be used to extend titanium dioxide is synthetic sodium alumino silicate. This pigment imparts comparable high brightness and opacity to paper at a lower cost than titanium dioxide.
Paper manufacturers are still, of course, in need of lower cost pigments than the synthetic sodium alumino silicates now being used but with equal or greater brightness and opacity when used in high quality papers and publication stocks.